Transfer of wild abortive cytoplasmic male sterility through protoplast fusion in rice
INTRODUCTION The genomes of two cytoplasmic organelles, plastids and mitochondria, encode such important traits as herbicide resistance or cytoplasmic male sterility (CMS), respectively. In higher plants, cytoplasmically-encoded traits are usually inherited maternally by crossing. However, in somatic cell fusion, the cytoplasms from both parents are also mixed as well as nuclei in a fused cell. In somatic hybrid or cybrid plants regenerated from fused cells, sorting out of one or the other parental chloroplasts and rearrangement of mitochondrial DNAs (mtDNAs) have been frequently observed (Maliga 1986). It is possible to create plants possessing novel organelle compositions. It has been also reported that the maternally inherited traits such as CMS were introduced through protoplast fusion in Nicotiana(Zelcer et ai.1978, Aviv et al. 1980, Medgesyetal.1985 Kumashiro and Kubo 198~ , Petunia (Boeshore et al. 1983) and Brassica(Pelletier et al. 1983, Yarrow et ai.1986, ~nczel et al. 1987). X-or gamma-irradiation of protoplasts is useful for the transfer of alien cytoplasmic traits through cell fusion. Since the irradiation treatment prevents colony formation from protoplasts and the irradiated nucleus is eliminated from a fused cell (Zelcer et al. 1987, ~nczel et al. 1982), cybrids are formed through protoplast fusion between irradiated cells (cytoplasm donor) and iodoacetate-treated cells (recipient) by metobolic complementation (Sidorov et al. 1981). We report here the selection of Daucus cvbrid plants with the double selection method, and show the successful transfer of a CMS trait. Mitochondrial genomes of those cybrid plants are also analysed.